Heat assisted narrow pole design with trailing shield

ABSTRACT

A TAMR (Thermally Assisted Magnetic Recording) write head is formed with a narrow pole tip, a trailing edge magnetic shield and, optionally, a plasmon shield. The narrow pole tipped write head uses the energy of laser generated edge plasmons, formed in a plasmon generating layer, to locally heat a PMR magnetic recording medium slightly below its Curie temperature, Tc. When combined with the effects of the narrow tip, this local heating to a temperature below Tc is sufficient to create good transitions and narrow track widths in the magnetic medium. The write head is capable of writing effectively on state-of-the-art PMR recording media having Hk of 20 kOe or more.

This is a Divisional application of U.S. patent application Ser. No.13/066,420, filed on Apr. 4, 2011, which is herein incorporated byreference in its entirety and assigned to a common assignee.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to the fabrication of magnetic read/write headsthat employ TAMR (thermally assisted magnetic recording) to enablewriting on magnetic media having high coercivity and high magneticanisotropy. More particularly, it relates to the use of a narrowmagnetic pole in conjunction with plasmon mode heating to obtain narrowtrack widths for recording at high densities.

2. Description of the Related Art

Magnetic recording at area data densities of between 1 and 10 Tera-bitsper in² involves the development of new magnetic recording media, newmagnetic recording heads and, most importantly, a new magnetic recordingscheme that can delay the onset of the so-called “superparamagnetic”effect. This latter effect is the thermal instability of the extremelysmall regions on which information must be recorded, in order to achievethe required data densities. A way of circumventing this thermalinstability is to use magnetic recording media with high magneticanisotropy and high coercivity that can still be written upon by theincreasingly small write heads required for producing the high datadensity. This way of addressing the problem produces two conflictingrequirements:

-   1. The need for a stronger writing field that is necessitated by the    highly anisotropic and coercive magnetic media.-   2. The need for a smaller write head of sufficient definition to    produce the high areal write densities, which write heads,    disadvantageously, produce a smaller field gradient and broader    field profile.

Satisfying these requirements simultaneously may be a limiting factor inthe further development of the present magnetic recording scheme used instate of the art hard-disk-drives (HDD). If that is the case, furtherincreases in recording area density may not be achievable within thoseschemes. One way of addressing these conflicting requirements is by theuse of assisted recording methodologies, notably thermally assistedmagnetic recording, or TAMR.

The heating effect of TAMR works by raising the temperature of a smallregion of the magnetic medium to essentially its Curie temperature (Tc),at which temperature both its coercivity and anisotropy aresignificantly reduced and magnetic writing becomes easier to producewithin that region.

In the following, we will address our attention to a particularimplementation of TAMR described in the prior arts, namely the transferof electromagnetic energy to a small, sub-micron sized region of amagnetic medium through interaction of the magnetic medium with thefield of an edge plasmon excited by an optical frequency laser.

The edge plasmon mode is excited in an overlap region between aconducting plasmon generator (PG) and a waveguide (WG). The source ofoptical excitement can be a laser diode, also contained within theread/write head structure, or a laser source that is external to theread/write head structure, either of which directs its beam of opticalradiation at the generator through a means of intermediate energytransfer such as an optical waveguide (WG). As a result of the WG, thelight optical mode couples to a propagating plasmon mode of a PG,whereby the optical energy is converted into plasmon energy. Thisplasmon energy is then transferred to the medium at the pole tip, atwhich point the heating occurs at a very small spot size. When theheated spot on the medium is correctly aligned with the magnetic fieldproduced by the narrow pole tip, TAMR is achieved. The following priorarts describe TAMR implementations in various forms.

K. Tanaka et al. (US Publ. Pat. Appl. 2008/0192376) and K. Shimazawa etat (US Publ. Pat. Appl. 2008/0198496) describe TAMR structures thatutilize edge plasmon modes to couple to a WG and then transmit andconcentrate the plasmon energy at the ABS (air bearing surface) of theTAMR head.

Harmann et al. (US Publ. Pat. Appl. 2005/0190496) discloses generating aheated spot on the leading edge side of a write gap.

Jin et al. (US Publ. Pat. Appl. 2007/0230047) teaches a TAMR writer witha narrow pole tip.

Poon et al, (US Publ. Pat. Appl. 2008/0154127) also discloses heating amagnetic media as it passes beneath a write gap.

Zhou et al. (US Publ. Pat. Appl. 2009/0052092) shows a small heatingcoil in a write gap.

Kasiraj et al. (U.S. Pat. No. 6,493,183) shows an electrically resistiveheater in a write gap between pole tips.

Lille (US Publ. Pat. Appl. 2010/0002330) describes a near field lightsource providing a pre-heating pulse using an optical waveguide.

The magnetic pole designs for TAMR application that are disclosed in theprior arts (such as those cited above) generally utilize a pole that ismuch wider than that being used in current (non-TAMR) perpendicularmagnetic recording (PMR) designs that address ultra-high areal density.The narrow track that is needed for such ultra-high areal density inTAMR is realized by the very small size of the heated spot when therecording is thermally dominant for a magnetic medium with a highcoercivity, such as FePt with L10 orientation.

As it is still in the development stage, FePt magnetic recording mediumsuffers from many adverse properties, such as roughness, large grainsize distribution, large variation in Tc (Curie temperature), largedHc/Hc and large switching field distributions. These properties, whentaken together, limit the linear density capability of the FePt mediumcompared to the state-of-the-art PMR medium that is granular CoCrPtbased. Improving the FePt medium for higher areal density recording asdesired might have a long way to go based on the current state of mediumdevelopment and medium evaluation. On the other hand, state-of-the-artPMR medium has been able to achieve >1500 kbpi linear density with goodSNR and BER and is likely to be improved even further to achieve evenhigher areal densities.

When conventional PMR media with low coercivity is used, a wide magneticpole and leading edge recording design will cause adjacent trackerasures as a result of the pole width (>300 nm). Thus, the head designsdisclosed in the cited prior arts will find it difficult to achieve thedesired high areal recording densities in conventional PMR media.

SUMMARY OF THE INVENTION

It is a first object of the present invention to achieve magneticrecording at high linear densities (>1500 kbpi) using currentlyavailable state-of-the-art PMR magnetic recording media with slightlyhigher Hk.

It is a second object of the present invention to produce such highareal densities while requiring only moderately elevated temperaturesthat are less than the Curie temperature (<Tc) of the recording mediaduring the recording process.

It is a third object of the present invention to achieve the first twoobjects while providing a pole design that does not create significantadjacent track erasures (ATE).

It is a fourth object of the present invention to fulfill the previousobjects with a head design that is uncomplicated and consistent withdesigns currently in use.

To meet these objects, we will address our attention to a particularimplementation of TAMR, namely the transfer of electromagnetic energy toa small, sub-micron sized region of a magnetic medium throughinteraction of the magnetic medium with the field of an edge plasmonexcited by an optical frequency laser. This energy transfer is providedwhile using a main write pole with a very narrow, shielded pole tip.Under these conditions, as will be described in detail below, thetransferred electromagnetic energy can cause the temperature of themedium to increase locally to values less than Tc, yet still besufficient to create good transitions within a state-of-the-art PMRrecording medium.

The edge plasmon mode is excited in an overlap region between aconducting edge plasmon generator (EPG) and a waveguide (WG). The sourceof optical excitement can be a laser diode, also contained within theread/write head structure, or a laser source that is external to theread/write head structure, either of which directs its beam of opticalradiation at the generator through a means of intermediate transfer suchas an optical waveguide (WG). As a result of the WG, the light opticalmode couples to a local plasmon mode of a propagating plasmon mode of aPG, whereby the optical energy is converted into plasmon energy. Thisplasmon energy is then transferred to the medium in the write-gap regionof the pole tip, at which point the heating occurs at a very small spotsize. When the heated spot on the medium is correctly aligned with themagnetic field produced by the narrow pole tip, TAMR is achieved.

The present invention will, therefore, disclose a heat-assisted narrowmagnetic pole with a trailing shield in which the heating spot isdelivered in the write gap by an edge plasmon generator. With thisdesign, magnetic dominant recording will occur, with a narrow track andconsequent higher track density, at moderately elevated mediumtemperatures that can be realized on current PMR media with a slightlyhigher Hk, in this case being an Hk of 20 kOe or more. Without thelocalized heating in the write gap, the writer field and gradientproduced by the narrow pole are not sufficient enough to switch themedium magnetization and write a good transition.

The TAMR writer design of the invention is one in which the pole has anarrow shape that permits high areal densities to be achieved in presentmagnetic media by means of thermally assisted writing at moderatelyelevated temperatures. Specifically, this design is a heat assistednarrow magnetic pole with a trailing shield (and supplemental plasmonshield) in which the heating spot is delivered in the write gap by anedge plasmon generator (EPG). The EPG is formed as a conducting layer (alayer of electrically conductive material) contiguous with the magneticcore of the pole tip itself, so the thermal energy of the plasmon andthe magnetic field of the tip can be closely aligned. The design of thehead structure is uncomplicated and permits trailing edge recording witha trailing shield and high magnetic field gradient. Since the heating isbelow Tc, less laser power is required and better thermal stability ofthe head structure is obtained. With the localized heating in the writegap, the writer field and the gradient produced by the narrow pole aresufficient to switch the medium magnetization and write a goodtransition.

BRIEF DESCRIPTION OF THE DRAWINGS

The objects, features, and advantages of the present invention areunderstood within the context of the Description of the PreferredEmbodiment as set forth below. The Description of the PreferredEmbodiment is understood within the context of the accompanying figures,wherein:

FIG. 1 is a schematic 3-dimensional drawing of the invention, showingthe narrow pole design, the plasmon generator, a trailing magneticshield and a plasmon shield.

FIGS. 2 a, 2 b and 2 c are schematic cross-sectional views of theinvention of FIG. 1. FIG. 2 a is a vertical cross-sectional side view,FIG. 2 b is a front cross-sectional view taken at a rear (distal to theABS) plane and FIG. 2 c is a front cross-sectional view taken at the ABSplane.

FIG. 3 is a schematic cross-sectional view at an ABS plane of analternative embodiment of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Each of the preferred embodiments of this invention is a shielded TAMRhead for producing high density recording on a currently available PMRmagnetic medium. The TAMR head incorporates an edge plasmon generator(EPG), a trailing magnetic shield, a plasmon shield for additionaloptical spot confinement and a narrow pole tip having leading edge andside tapers that extends between approximately 0 nm-100 nm into the ABSto concentrate the magnetic flux.

Optical energy is supplied by a laser, directed through a waveguide (WG)as a diffraction-limited waveguide mode to the EPG, where it excites aconfined edge plasmon mode by evanescent coupling at the overlap regionbetween the WG and the EPG. The edge plasmon mode propagates along theedge of the EPG and finally delivers its energy to the ABS and heats upthe medium locally in the write gap region of the ABS.

First Embodiment

Referring to schematic FIG. 1, there is shown a 3-dimensional view ofthe heat assisted magnetic write pole with a narrow pole tip design ofthe present invention. An optical waveguide, WG, (10) is positionedadjacent to (and separated from) the trailing edge side of the main pole(MP) (20). The shape of the MP (20) shows an upward sloped leading edgetaper (25) and downward sloped side tapers (27). An edge plasmongenerator (EPG) (30) is formed as a conducting layer conformallycovering a substantial portion of the trailing edge of the MP, which canhere be considered as extending over the side tapers (27). Note alsothat although the EPG has a thickness between approximately 5 nm and 80nm, the thickness is not shown in this perspective drawing.

The region of coverage by the EPG, which includes coverage over thesymmetric sides (27) of the MP and over the entire trailing edge surfaceof the narrow pole tip (40), overlaps with, but is separated from, aportion of the WG above it. It is at this overlap region at which theedge plasmon mode is excited in the EPG by the WG.

The main pole (20) with its narrow projecting pole tip (40), NP, isformed as a single piece of magnetic material such as Ni, Fe, Co andtheir alloys. The NP (40) extends outward from the ABS end of the bodyof the main pole (20) in the direction perpendicular to the ABS plane,for a distance (denoted the neck height, NH, of the pole tip) of betweenapproximately 0 nm and 100 nm to concentrate the magnetic flux at themagnetic medium. At its ABS end, the width of the pole tip is betweenapproximately 5 nm and 80 nm along the cross-track direction, the lengthof the pole tip along the down-track direction (base-to-peak in thefigure) is between approximately 50 nm-200 nm and the radius (height oftriangular portion) of the pole tip peak is between approximately 2 nmand 20 nm.

The EPG (30) conformally covers the peaked trailing edge of the NP. Inthis preferred embodiment, the ABS shape of the narrow pole tip is arectangle with a peaked (triangular) upper (i.e., trailing edge)portion. A trailing edge shield (50), TS, is formed at the ABS of theWG, at the trailing edge side of the pole tip. The trailing edge shieldis formed of magnetic materials such as Ni, Fe, Co and their alloys andits dimensions are between approximately 200 nm-500 nm in they-direction, between approximately 300 nm and 2000 nm in the z-directionand between approximately 50 nm-200 nm from the ABS (the x-direction). Aplasmon shield (60), PS, is formed on the leading edge of the trailingedge shield. The plasmon shield, which is formed of noble, highlyconducting metal such as Au, Ag, Cu and their alloys, has dimensions ofbetween approximately 10 nm and 100 nm in the cross-track direction,between approximately 50 nm and 500 nm in the down-track direction andbetween approximately 50 nm and 200 nm from the ABS. The plasmon shieldis used to further confine the optical spot produced by the EPG layer byshunting the electric field of the plasmon mode.

Referring now to FIG. 2 a, there is shown a schematic sidecross-sectional view of the write pole structure in FIG. 1. Thecross-section is along the center plane of the structure and it passesthrough the peak of the MP (20) and NP (40). There is shown the waveguide (10), with the trailing edge shield (50) at its ABS end (the ABSbeing indicated by a dashed line). There is also seen the sidecross-section of the MP (20) with the NP (40), extending from the end ofthe MP to the ABS for the neck-height, NH, distance. The leading edgetaper (25) is shown with the NP at its ABS end. The cross-section of theEPG layer (30) is shown on the trailing edge surface of MP (20) and overthe narrow pole tip (40) as well.

Thus, the EPG can be said to have a magnetic core (the pole material)from which the writing magnetic field emanates while the heating energyof the edge plasmon emanates from the EPG layer. The region of overlapbetween the WG and the EPG (which is the entire length of the EPG shownhere) is the region within which the optical mode of the WG couples withthe edge plasmon mode in the EPG.

Referring next to schematic FIG. 2 b there is shown the horizontalcross-sectional view of FIG. 2 a, taken through a plane parallel to butdistal from the ABS plane. This plane is marked at its edge by thevertical dashed line 1-1 in FIG. 2 a, which is at the back-end (distalend) of the main pole (20), away from the narrow pole tip, where thepeaked, trailing edge surface is largest. The EPG layer (30) is shownconformally covering the trailing edge surface of the MP at this backend. The WG (10) is shown above the EBG layer (30), separated from it(not in contact) along the overlap region. According to FIG. 2 a, theoverlap region extends between the ABS and the 1-1 plane, which is thecross-sectional plane of FIG. 2 b.

Referring finally to schematic FIG. 2 c, there is shown a horizontalcross-sectional view of the structure in FIG. 2 a, taken through the ABSplane of the narrow pole tip. There can be seen the trailing shield (50)(the plasmon shield is not shown) and the ABS peaked shape of the narrowpole tip (40) covered conformally by the EBG layer (30). It can be seenthat the system behaves as a conducting EPG layer conformally covering amagnetic core. The cross-track (y-direction) width of the NP (shown as adouble headed arrow labeled PW) can be between approximately 5 nm and 80nm, depending on the track density required. The EPG layer can be formedof Au, Ag or their alloys, which is deposited on the magnetic pole(here, of triangular shape) formed by IBE or similar etching process toa thickness of between approximately 5 nm and 80 nm. The pole tip isalso etched, together with the EPG, to achieve its width as well as itsshape. If the surface area of the tip at the ABS is too small, theconfined edge plasmon mode may “leak” out because the boundaryconditions become inadequate for confinement, in which case the overalloptical efficiency of the system will be reduced.

Second Embodiment

Referring to schematic FIG. 3, there is shown an alternative structurethat forms a second embodiment of the invention. In this design, themagnetic pole is still tapered down to a narrow tip (200) of magneticmaterial at the ABS, but the EPG layer (30) retains the samecross-sectional dimension from the back end of the pole where itcommences (i.e., as is shown in FIG. 2 (b) for the first embodiment), tothe ABS end (which is shown here in FIG. 3). The trailing shield (50) isshown above the pole tip. Maintaining the dimensions of the EPG layer isaccomplished by filling the region around the etched pole tip withnon-magnetic metals (220), such as Ta, Ti, Ru, Cr or any of theircomposites, to provide support for the EPG layer. It is to be noted thatFIG. 3 is analogous to FIG. 2( c), in that it illustrates the ABS end ofthe pole in this second embodiment, just as FIG. 2( c) illustrates theABS of the pole in the first embodiment. Superficially, FIG. 3 may looklike FIG. 2( b), which shows the back end of the first embodiment, butthis is because the EPG layer retains its shape from back to front.Thus, the magnetic portion of the pole tip may be diminished in surfacearea and cross-sectional area, but the EPG layer can still retain itscoverage because it is supported from beneath by the non-magneticmaterial (220) filling a region surrounding the pole tip laterally. Thewaveguide (50) is shown above the pole.

An exemplary process to form this structure would require first etching(eg., an IBE) of the magnetic pole to create the narrow portion of thepole tip, shown here as a rectangular prism with a triangularroof-shaped upper portion, and then depositing the non-magnetic metaluniformly and symmetrically around the etched tip. Then a second IBE(for example) will form the triangular shape with the sloped sidewall byetching away the deposited non-magnetic layer from the slopingtriangular sides of the pole tip, leaving horizontally extendingportions to either side of the pole tip. Finally, the EPG material isdeposited as a layer over the composite formation of magnetic andnon-magnetic materials, which supplies sufficient physical support forthe EPG layer.

Mathematical modeling of the spot size produced by an EPG layer formedover a 50 nm pole tip with a magnetic trailing shield shows that a spotsize of 50 nm can be achieved. Further modeling has been done to comparethe recording patterns of different head designs and media. By using thePMR media with Hk=20 kOe (kilo-Oersteds), at a temperature of 575 K,which is less than the media Tc of 650 K, the present invention writesthe best transitions with the narrowest tracks. Without heat assistance,the writability of PMR becomes weaker as the pole tip is scaled down toachieve greater track densities. A conventional PMR writer (producing noheating) can write good transitions in low Hk media (Hk≈15 kOe), but thetrack becomes wider. In particular, the transitions caused in FePt mediaare poorer when a leading optics TAMR design is used, but with a widerpole width. Overall, the disclosed heat assisted narrow magnetic poledesign of the present two embodiments, including the trailing shield, isable to write better transitions with narrower track width into granularCoCrPt based magnetic medium by moderately elevating the medium withhigher Hk.

As is understood by a person skilled in the art, the preferredembodiments of the present invention are illustrative of the presentinvention rather than being limiting of the present invention. Revisionsand modifications may be made to methods, processes, materials,structures, and dimensions through which is formed and used a trailingedge shielded, surface plasmon generating TAMR write head with a narrowpole tip producing a heating spot in the write gap a recordingtemperature less than Tc in state-of-the-art recording media, whilestill providing such a TAMR write head, formed and used in accord withthe present invention as defined by the appended claims.

What is claimed is:
 1. A method of forming a TAMR (thermally assisted magnetic recording) write head comprising: providing a magnetic write pole; using a first etching process, etching a narrow tip at an ABS end of said write pole, said narrow tip being a rectangular prism having a cross-sectional shape in an ABS plane comprising a rectangle capped at a trailing edge side by a triangular peak having a base width equal to the width of said rectangle; depositing a non-magnetic layer over said narrow tip, said layer covering said triangular peak and extending laterally and symmetrically to both sides of said narrow tip; using a second etching process, etching said non-magnetic layer to remove that portion covering said triangular peak but leaving a remaining portion abutting both lateral sides of said rectangular portion, said remaining portion sloping downward to form a continuation of said triangular peak and thence extending horizontally laterally and symmetrically; then forming a plasmon generating layer contiguously over exposed trailing edge surfaces of said narrow pole tip and said non-magnetic layer.
 2. The method of claim 1 wherein the width of said narrow tip is between approximately 5 nm-80 nm in a cross-track direction, wherein the length of said narrow tip along a down-track direction is between approximately 50 nm-200 nm and wherein the radius of a peak of said narrow pole tip is between approximately 2 nm and 20 nm.
 3. The method of claim 1 wherein said non-magnetic layer is formed of Ta, Ti, Ru, Cr or their composites.
 4. The method of claim 1 wherein said plasmon generating layer is a layer of Ag, Au or Cu and is formed to a thickness of between approximately 5 nm and 80 nm.
 5. The method of claim 1 including the formation of a leading edge shield formed of the magnetic materials Ni, Fe, Co and their alloys having dimensions between approximately 200 nm and 500 nm in a cross-track direction, between approximately 300 nm and 2000 nm in a down-track direction and between approximately 50 nm and 200 nm from the ABS.
 6. The method of claim 5 further including the formation of a plasmon shield on a leading edge of said trailing edge shield.
 7. The method of claim 6 wherein said plasmon shield is formed of the highly conducting metals Au, Ag, Cu and their alloys and has dimensions of between approximately 10 nm-100 nm in the cross-track direction, of between approximately 50 nm-500 nm in the down-track direction and of between approximately 50 nm-200 nm from the ABS.
 8. A method of forming a TAMR (thermally assisted magnetic recording) write head comprising: providing a magnetic write pole; using an etching process, etching a narrow tip at an ABS end of said write pole, said narrow tip being a rectangular prism having a cross-sectional shape in an ABS plane comprising a rectangle capped at a trailing edge side by a triangular peak having a base width equal to the width of said rectangle; then forming a plasmon generating layer contiguously over exposed trailing edge surfaces of said triangular peak portion of said narrow pole tip.
 9. The method of claim 8 wherein the width of said narrow tip is between approximately 5 nm-80 nm in a cross-track direction, wherein the length of said narrow tip along a down-track direction is between approximately 50 nm-200 nm and wherein the radius of a peak of said narrow pole tip is between approximately 2 nm and 20 nm.
 10. The method of claim 8 including the formation of a trailing edge shield formed of the magnetic materials Ni, Fe, Co and their alloys having dimensions between approximately 200 nm and 500 nm in a cross-track direction, between approximately 300 nm and 2000 nm in a down-track direction and between approximately 50 nm and 200 nm from the ABS.
 11. The method of claim 10 further including the formation of a plasmon shield on a leading edge of said trailing edge shield.
 12. The method of claim 11 wherein said plasmon shield is formed of the highly conducting metals Au, Ag, Cu and their alloys and has dimensions of between approximately 10 nm-100 nm in the cross-track direction, of between approximately 50 nm-500 nm in the down-track direction and of between approximately 50 nm-200 nm from the ABS. 